Generally, tubular or hose-type medical devices, so-called “stents,” are employed as endoprostheses for the treatment of dysfunctions of hollow spaces or cavities in a living organism. Stents usually comprise a wire cage and are intended as a guide rail type reinforcement or support of hollow bodies in humans or animals. Typical fields of application include a vascular system, a gastrointestinal system, and a urinary system, for example. Usually, stents are applied in a compressed condition with the aid of a suitable delivery instrument, like a catheter or a trocar, for example, through the hollow body to be treated up to the intended treatment site and released there. Deployment of the stent provided in a compressed state in the delivery instrument is effected by inherent spring reset forces, due to the stent design principle, or by means of balloon dilatation. What is essential is that the stents will endure dynamic and static deformation over a long time without suffering appreciable loss of their original restoring forces. An ideal case prerequisite is that the stent will conform to the place of application relative to a lumen of the human or animal hollow body to be treated as well as relative to flexibility of the treated region and will remain in the living body as a permanent device.
An example of the above-described stents relates to so-called “stent-grafts.” A stent-graft is a tubular device composed of a special fabric supported by the rigid structure of a stent. Stent-grafts are typically configured by separately forming the graft and the stents, and then attaching the graft to the stents. To attach a stent to a graft, the graft is typically inserted into, or pulled over the stent, and the graft is sewn to the structural components of the stent. Alter-natively, the stent may be formed on the graft such that by way of example the individual wires of the stent are threaded through specially provided projecting fabric loops on the surface of the graft, thereby facilitating attachment of the graft to the stent.
However, attachment of the graft to the stent in the above described ways may often result in an undesired bulk requiring a delivery system of a large diameter. Further, attachment of the graft to the stent, normally by sewing, may provide potential sites for undesirable leakage of body fluids, in particular blood, through the graft structure. A further disadvantage relates to the interior wall of these stent grafts. Due to the stent wires projecting from the fabric of the graft, the interior wall is usually not smooth, but profiled. Due to the profile of the interior wall, adherence of blood components may occur to the inner wall of the stent-graft, thereby increasing the risk of forming a thrombosis and subsequent restenosis.
WO 2008/112242 A2 discloses a stent-graft based on a Nitinol wire and textile strands. For the production of such a stent-graft, the Nitinol wire is first shape set into a required shape. Then, such shape set Nitinol wire is processed together with the textile strands to obtain the stent-graft. This approach is probably employed since process engineering of the stent-graft under high temperatures (the conventional heat treatment of Nitinol is performed at temperatures between 560 and 580° C.) is complicated. In particular, the usage of numerous potentially qualified fiber materials is precluded by such elevated temperatures. Another withdrawal relates to a reduced adhesion among the Nitinol wire and the textile strands resulting in an increased displacement mobility between the Nitinol wire and the textile strands leading to an increased risk for leakage to occur during use of such a stent-graft.
It could therefore be helpful to provide an improved medical device to overcome the shortcomings of conventional stents or stent-grafts, in particular in relation to leakage, interior profile, the occurrence of thrombosis or restenosis, equally capable of enduring dynamic and static deformations over a long time, without appreciable loss of its original radial expansive pressure. Furthermore, the medical device should be produced in a most simple way and applied medically under gentle conditions.